How are exposed PCB's safe?

I've noticed a lot of PCB based products like the Beagleboard, Beaglebone, Arduino, Raspberry Pi don't come in enclosures by default. Isn't this fatal for them? Maybe the manufacturer has an unwritten rule that you're supposed to buy an enclosure but for new devices like the Pi there are no enclosures.

So how do you use them without losing them due to static electricity or inadvertently causing any kind of damage to them? If there were an enclosure, is that good enough or is there something that is necessary in the enclosure in order to protect it from static electricity? Does it have to be grounded with rubber grommets or something where the actual PCB meets acrylic for example?

Mechanically, those devices are surprisingly tough. The tiny fragile components are also very flat to the board, so there's not enough mechanical advantage to knock them off unless you really grab and pry them up. A hard hit to the side of a small passive component might shear it off of the board, but that'd be a pretty precise hit. The USB/UTP connectors are, for obvious reason, designed to be very secure. Even the surface mount versions of those connectors, with a proper footprint on a quality double-sided PCB, are very robust. In fact, pretty much every piece of consumer electronics out there has no mechanical support for those sorts of connects aside from what's provided by the PCB. Even with the added leverage of a cable plugged in, it should take some effort to damage the connector. Probably the most vulnerable components are the header connectors, but even then those are usually through-hole and so hard to dislodge. You might bend a few pins on an unshrouded male header, but those are easily bent back. You also have the threat of scratching/gouging the PCB damaging traces, and that's really dependent on the quality of the PCB. As far as I've seen, all of the products you've mentioned use FR4 laminate with full solder mask, which does a surprisingly good job at being resilient to that sort of damage. It would take a pretty sharp tool and some effort to damage a trace.

As for ESD, the real vulnerable time for components is before they're placed on the PCB, where there's the greatest chance of a discharge taking a harmful path through the device. Empirically, it doesn't seem to be a big threat, at least at levels that are measurable in the market for these kinds of devices. Someone else can probably give a better explanation of that, though.

Anyone who has worked in semiconductor failure analysis has seen the evidence of electrical overstress from ESD. It is no myth.ESD may kill a device immediately or it may just start processes that kill the device after a period of use. So you may not see a direct correlation between an ESD event and immediate failure and you may not recognise that you have killed the device but it will fail at some time in the future as a result.

The short answer is that they aren't safe. But the failure rate is low enough for the manufacturer to leave it to the owner to deal with. And for cheap devices, there is much pressure to keep things inexpensive and to not include safety features that add cost.

I've been working with and fixing IT and electronics for 20 years+. I've never killed anything by ESD.

ESD is pretty much an old wive's tale as far as I'm concerned. Worst I've had is a bit of a zap to a motherboard, which made the machine reboot and continue merrily on.

I have, but it has been exceptionally rare, and even rarer that I've witnessed an immediate kill.

I've also seen motherboards (more than 1) killed by hot plugging mice or keyboards in via the PS/2 connectors - again, exceptionally rare, but it can happen.

That said, I'm not nearly as cautious with ESD as I probably should be. When working on my own stuff I don't wear straps or use ESD mats or anything, I just make sure I'm grounded before I touch anything or ensure that I'm at the same potential as any case the PCB may be mounted in before I touch the PCB itself.

As for stuff like Arduino - I'm aware I could subject mine to ESD death since it's sitting here unprotected, but IME, the chances of that happening are extremely minor. I'm well aware that they're not zero, but given the cost of replacement should I kill it (roughly $30 shipped), it's just not a pressing concern.

I'd feel differently if the probability of an ESD kill was orders of magnitude higher, or the cost of the equipment was much greater than it is. But ESD death is unlikely, and even if it happens, it's not particularly expensive to replace.

Ahahaha, I meant PCB as in printed circuit boards. Not just bare circuit boards though, ones with components already placed on them.

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Motherboards don't come with cases/enclosures, so I don't see why PCB devices like Raspberry Pi has to come with one.

Yeah but it's pretty much implied that they'll go into a case. That isn't implicit in something like the Raspberry Pi or Beagleboard (there are enclosures for the latter). There's more people putting their mobo's in cases then there are people leaving their mobo's out on cardboard and running their PC's without a case at all.

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Plus, traces these days for multi-layer PCBs are laminated.

What does this mean? You mean how the surface of the PCB is covered in a thin layer of plastic or something? Is that why the traces are colored and not showing bare copper?

Based on the answers I wish I could just not care but I wish I could not be wrong as well. It's true I could just get another Raspberry Pi or Arduino but I'd rather not kill them in the first place if it means I can buy a cheap enclosure.

Anyone who has worked in semiconductor failure analysis has seen the evidence of electrical overstress from ESD. It is no myth.ESD may kill a device immediately or it may just start processes that kill the device after a period of use. So you may not see a direct correlation between an ESD event and immediate failure and you may not recognise that you have killed the device but it will fail at some time in the future as a result.

Seconded.

Take two trays of parts and subject one batch to very low levels of ESD - I mean levels in the tens of volts, far too low to feel as a shock. You will almost certainly not see any immediate failures. But run those parts through stress testing and you'll find they have a higher failure rate than the control group.

(this is not theoretical. This experiment has been done many many times since the first ESD problems were noticed with the first MOS transistors. The results continue to be as described above.)

Yes, the chips have ESD protection built in. And that keeps getting better. But at the same time, the feature size on the ICs keeps getting smaller. The smaller the feature size, the more susceptible to ESD.

Electronics manufacturers spend significant coin to minimize ESD. Electronics manufacturers, like everyone else, are constantly on the lookout for ways to reduce their costs. They wouldn't be taking the anti-ESD measures if they weren't proven to be effective.

What does this mean? You mean how the surface of the PCB is covered in a thin layer of plastic or something? Is that why the traces are colored and not showing bare copper?

Yes. It's called solder mask or solder resist. The primary purpose is to prevent solder bridges between adjacent traces/pads/leads (especially during wave soldering), but it has the added advantage of protecting the copper from oxidation and accidental short circuits, and generally making for a more resilient board.

PCB's are actually surprisingly resilient. Waaaay back in the good ol' days I helped a friend over a weekend make up some custom ISA controller cards in his garage. We prepped all the components, applied flux and hot-dipped them in a solder bath then set them to cool. I noticed that the PCB's still had a fair amount of flux on them and asked how we would clean them off. Turned out that he just set them in the racks of his kitchen dishwasher and ran it a cycle without any soap. Afterwards we cleaned the remaining water off with compressed air, removed protective tape from some DIP switches and then verified that they worked properly.

That was a big lesson to me at just how hardy most electronics could be. Granted, while ESD is something to take precautions for, as long as you mount a board so that the soldered connections can't ground out they should be just fine. You mean you've never seen a motherboard working in mineral oil before?

Granted, while ESD is something to take precautions for, as long as you mount a board so that the soldered connections can't ground out they should be just fine. You mean you've never seen a motherboard working in mineral oil before?

These concepts have nothing to do with each other. Mineral oil is nonconductive; electrically speaking such a mobo might as well be suspended in air. And ESD damage does not depend on the soldered connections being grounded. Or not grounded. Although, if you did manage to ground ALL of the connections to a chip, you would preclude ESD damage to that chip.

ESD is pretty much an old wive's tale as far as I'm concerned. Worst I've had is a bit of a zap to a motherboard, which made the machine reboot and continue merrily on.

It really depends on climate. Here in Houston, there's basically no chance of a static discharge of any kind for 9 months out of the year (60-100% humidity). OTOH, I have been places where you couldn't open a door after walking across a carpeted room without a visible spark. ESD can be an issue, but in most single instances it's not.

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So how do you use them without losing them due to static electricity or inadvertently causing any kind of damage to them?

As far as other kinds of damage, PCBs and the stuff on them are generally extremely tough, despite what they look like. You are far more likely to hurt yourself than the electronics. I can't remember ever breaking something off a PC motherboard (built and maintained them in an IT department for years), but I have plenty of little scars on my hands.

PCB's are actually surprisingly resilient. Waaaay back in the good ol' days I helped a friend over a weekend make up some custom ISA controller cards in his garage. We prepped all the components, applied flux and hot-dipped them in a solder bath then set them to cool. I noticed that the PCB's still had a fair amount of flux on them and asked how we would clean them off. Turned out that he just set them in the racks of his kitchen dishwasher and ran it a cycle without any soap. Afterwards we cleaned the remaining water off with compressed air, removed protective tape from some DIP switches and then verified that they worked properly.

This is actually how it was done in small factory I worked at for a while, except that instead of a regular dishwasher it was a bigger, industrial washer with a separate dryer, but the same idea. The washing process has nothing to do with ESD, in fact it's not dangerous to most electronics at all unless you have a charged cap or a battery installed for some reason (pro-tip: don't). I knew a few people in the suppressor department who worked without ESD straps whenever they could (or goggles; I was never without both if I could help it), but those boards were basically just rows of high-energy varistors, and all the workspaces had anti-static mats. The floor was also partially constructed to minimize ESD, but it was no substitute for bracelets or footstraps during the winter. ESD damage did cause some rejections of other circuit boards in Quality Assurance, which ensured that the higher-ups would tour the floor and get people religious about ESD straps (until next time). I've seen it happen enough that I would definitely worry about being grounded when working on something that A) I'm being paid for, or B) I paid a decent buck for. If it's just some $20 kitbag of parts I usually don't sweat it.

I've noticed a lot of PCB based products like the Beagleboard, Beaglebone, Arduino, Raspberry Pi don't come in enclosures by default.

All of the components you have listed are raw components, not completed solutions. They are simply parts that you can build prototypes of whatever you want out of. The beauty of these things is that they are usable in a myriad of applications, and that usefulness would be greatly diminished if they were (by default) sold in enclosures.

An enclosure is just a peripheral to these devices (like sensors, motors and displays) that the user gets to pick what ever they want to use. (and you are correct that end-users should use some form of enclosure that insulates it from environmental issues like ESD, etc.)

Anybody who buys raw components like an Arduino or Rasberry Pi should not expect it to be a finished all-in-one product like an iMac that is hardened against hurting stupid consumers or being harmed by them.

When you enter the world of raw components, you leave the world of hand-holding customer support and freebie warranty repairs when you break things, and you assume the responsibility of making sure that your device has adequate safety and shielding.

PCB's are actually surprisingly resilient. Waaaay back in the good ol' days I helped a friend over a weekend make up some custom ISA controller cards in his garage. We prepped all the components, applied flux and hot-dipped them in a solder bath then set them to cool. I noticed that the PCB's still had a fair amount of flux on them and asked how we would clean them off. Turned out that he just set them in the racks of his kitchen dishwasher and ran it a cycle without any soap. Afterwards we cleaned the remaining water off with compressed air, removed protective tape from some DIP switches and then verified that they worked properly.

This is actually how it was done in small factory I worked at for a while, except that instead of a regular dishwasher it was a bigger, industrial washer with a separate dryer, but the same idea. The washing process has nothing to do with ESD, in fact it's not dangerous to most electronics at all unless you have a charged cap or a battery installed for some reason (pro-tip: don't).

Back in the '90s, several entrepreneurs made money by buying non-functional PC components cheap in bulk(both mechanical things like floppy drives and circuit-board stuff like motherboards and ISA/PCI cards), putting them in a regular dishwasher with mild soap and no rinse agent and then drying them in a consumer-level kitchen oven with a digital temp gauge that could keep it at the critical temp range that would evaporate the water, but not roast the circuit board or any plastic parts (IIRC, 140F-160F). (There was plenty of discussion on which soaps worked best, and what temperatures worked best.) They would then retest them, and sell the numerous components that were revived by the process. I heard rumors that 50-75% of the devices they washed like this would revive. Back when a floppy drive might sell for $99 new in 1995 money, they made a killing buying "junk" for pennies on the dollar and selling the fixed parts for 50% off new prices.

An enclosure is just a peripheral to these devices (like sensors, motors and displays) that the user gets to pick what ever they want to use. (and you are correct that end-users should use some form of enclosure that insulates it from environmental issues like ESD, etc.)

Anybody who buys raw components like an Arduino or Rasberry Pi should not expect it to be a finished all-in-one product like an iMac that is hardened against hurting stupid consumers or being harmed by them.

When you enter the world of raw components, you leave the world of hand-holding customer support and freebie warranty repairs when you break things, and you assume the responsibility of making sure that your device has adequate safety and shielding.

Well duh (to me), I don't know why I blanked that part out. I knew people used them for projects it just never connected as a reason as to why they don't come with enclosures by default. Now that I think about it, it does explain why they don't come with enclosures by default. Someone could be using them for a project that doesn't need an enclosure, it would be a waste to supply an enclosure to everyone when they might end up binning them because they intend the Arduino for example to go right into the project. I guess I just wish they sold some enclosures at release instead of waiting for third parties to make and sell them, but this really can't be helped I think. I know Raspberry Pi will have a first party enclosure and all units will be sold with enclosures by Summer.